Uniform, Filamentary, and Striped Patterns in Helium Dielectric Barrier Discharge Cryoplasmas

Dielectric barrier discharge cryoplasmas were generated in helium at temperatures between 192 K and 7.6 K at pressures between 1.2 × 10
⁵
and 5.2 × 10
³
Pa. Different discharge structures were observed, such as uniform glow, filamentary, and striped patterns, whose formation depends on the neutral gas temperature, applied voltage, and frequency. At higher temperatures, in addition to He, optical emission spectra include bands due to impurities such as N
₂
, while at temperatures below 20 K, only peaks due to He and He
₂
are observed.